Natural killer (NK) cells are lymphocytes that serve important functions in defense against disease and maintenance of health. Several characteristics of NK cells make them an excellent model to pursue studies in intracellular signaling and cytoskeletal biology and their relation to immune function. These include a well characterized set of inhibitory receptors that downregulate cell activities through phosphatase activity and specific activating receptor-induced kinase pathways having notable distinctions from those in other lymphocytes. The candidate presents preliminary data suggesting that cytoskeletal regulatory processes are important to NK cell function. Studies of patients with Wiskott-Aldrich syndrome (WAS) having a mutation in the gene encoding the WAS protein (WASp) have proven particularly useful in this regard. WASp, which promotes the branching of actin networks, was found to accumulate with filamentous actin at NK cell activating immunologic synapses and intact WASp function was required for actin rearrangement and NK cell function. It is likely that the deficits found in NK cells of patients with WAS contribute to their clinical presentation. The studies proposed in this application will test the hypothesis that the regulation of cytoskeletal activation in NK cells is a critical process for the induction and inhibition of NK cell function. In particular, the investigator proposes: 1) certain key intracellular signaling events link activating receptor ligation to cytoskeletal activation and function in NK cells; 2) there is a critical interrelationship between the actin cytoskeleton and microtubular network in NK cells; and 3) the cytoskeleton is a target of NK cell inhibitory receptor-mediated inhibition of NK cell function. These studies hold the potential to uncover novel pathways of cytoskeletal regulation and address the interdependence of cytoskeletal events leading to immune cell function. The candidate has an extensive background in mouse cellular immunology and in vivo immune responses. By undertaking this project he will develop skills in biochemistry and become proficient in the investigation of intracellular signaling. Furthermore the candidate will greatly expand his molecular biology capabilities and continue to gain proficiency in human cellular immunology. The applicant will be mentored in these efforts by Dr. Raif Geha, an authority on immunodeficiency as well as the cytoskeleton as it relates to immune function, and Dr. Jack Strominger an expert in natural killer cell biology and biochemistry. Ultimately, the candidate plans to use his position as a pediatric immunologist to better understand NK cell function and the role NK cells play in maintenance of human health.